1. Field of the Invention
The present invention is broadly concerned with processes for the production of hybrid proteins formed by the interprotein and/or intraprotein rearrangement of SS/SH bonds in a plurality of different starting proteins, in order to obtain hybrid proteins having desired functional characteristics. More particularly, the invention is concerned with such processes and the resultant hybrid proteins wherein an aqueous, protein-containing slurry comprising at least two different proteins is initially homogenized and then hydrothermally treated using high pressure steam in a jet cooker or similar device in order to cause an interaction between steam and the starting proteins, thereby altering the conformance of at least some of the proteins. The treated slurry is then held and cooled to cause the formation of hybrid proteins, which are recovered by spray drying or any other moisture removal technique.
2. Description of the Prior Art
Proteins are essentially composed of linear chains of amino acid residues linked together by peptide bonds which join the nitrogen atoms of amino groups to the carbon atoms of preceding carboxyl groups. All amino acids have identical backbone structure and differ only in their side chains. The physiochemical properties of amino acid residue side chains and the sequence of these residues are the dominant factors in determining the structure and function of proteins. Protein molecules also vary widely in size, e.g., enzymes may vary in size from about 13 kDa up to several thousand kDa.
The structure of proteins is recognized at four distinct levels of importance. The most basic level is the primary structure, i.e., the sequence of amino acid residues in the chain. The secondary structure of proteins relates to the conformation of amino acid residues which are relatively close to one another in the chain. Three conformations are known: α-helix, β-pleated sheet and a periodic (also known as random coil). The tertiary structure of proteins refers to the spatial structure thereof, resulting from hydrophobic and electrostatic forces, and disulfide bridges between aliphatic and aromatic side chains of the protein. Hydrophobic interactions are the major forces responsible for tertiary structure. The fourth and last protein structure is quaternary structure. This essentially describes the nature of the assemblage of protein subunits to form a massive aggregated molecule.
The properties of food and proteinaceous feed ingredients may be placed in two categories, namely nutritional and functional properties. Functional properties are defined as those properties of a food or food ingredient that affect its utilization, or influence the behavior of the food or food system during processing, handling, storage, preparation and consumption. For a given protein to perform well in a food system, it should normally possess multiple functionalities. For example, egg white possesses multiple functionalities including foaming, emulsifying, heat setting, and binding/adhesion. The functional properties of any protein are basically related to its physiochemical and structural properties including size, shape, amino acid composition and sequence, net charge, charge distribution, hydrophobicity/hydrophilicity ratio, and the secondary, tertiary and quaternary structural arrangements.
Efforts have been made in the past to modify or rearrange proteins in order to alter the functional properties thereof. For example, European Patent No. 782825 describes a method of rendering whey protein more hydrophobic in order to improve its gelling properties. Commercially available whey protein concentrate was heated to 75° C. along with sodium or magnesium caseinate, giving the resultant protein an increase in hydrophobicity. Lasztity et al., Narung, 42:210 (1998) studied wheat germ protein systems modified with urea to disassociate quatemarystructures, β-mercaptoethanol to reduce SS bonds and aeration to reoxidize SH groups to SS bonds. This treatment altered the surface protein properties of the wheat germ protein.
The dissertation of Ballegu, Effect of Hydrothermal Process on Functional Properties of Wheat Gluten Isolate (2001), describes hydrothermal processing of wheat gluten isolate using a jet cooker. HPLC profiles of the recovered protein samples revealed polymerization of gliadin molecules through aggregation and/or crosslinking to give glutenin or glutenin-like molecule; the extent of polymerization was found to depend upon the process severity. The viscosity of the hydrothermally processed wheat gluten isolate was found to be higher than that of the control, regardless of processing conditions.
Other references include: Cosio et al., J. Dairy Sci., 83:1933 (2000); Apichartsrangkoon, Food Sci., 67:653 (2002); U.S. Pat. Nos. 4,038,431, 4,500,454, 3,754,926, 5,100,679, 5,068,117, 4,036,996, 3,965,268, 4,038,432, 4,062,987, and 4,650,856; and Japanese Patents Nos. 356021568, 362146659, 361227739 and 360030645.
Generally speaking, the prior art teaches that single proteins or mixtures may be modified by processes using chemical modifiers together with heat and pressure (e.g., extrusion or steaming processes). However, such techniques can profoundly alter the functional properties thereof, sometimes in disadvantageous ways.